I'm an avid mountain biker and after my last no-name bag fell apart on the trail after just 2 months, I decided to go with something I thought would be better quality. I bought the medium Bontrager Pro Seat Pack. The features were great. I loved the inside pockets and the size was just right. Unfortunately, it didn't last much longer than my previous cheep-o bag because the zipper broke and I ended up losing my innertube patch kit on the trail. There's no way to repair the zipper and now I'm out more money and back to looking for a better seat pack.

I carried a tube and co2 cartridges I. The seat bag and on one ride the zipper broke so I took it back got a new one easy on another ride it happened again and again and again about 5 times the zipper piece would actually stretch and fatigue cause it was a cheap pile of junk

It fits my odd-shaped suspension seatpost! The XL looks to be the same size as the large but it's got a zip out extension so it will hold more. In its normal config, w/o zip out, I got 2-700c tubes, patch kit, tire levers, multi-tool, electrical tape, zip ties, pressure gauge, MTB headlight, etc to fit comfortably. And it doesn't look THAT big.

I removed the internal webbing that keeps the zipper flap from opening all the way. It makes it easier to add and remove the items.
The one I purchased was too small, so I'm probably going to purchase a larger one to fit my tube, tools, and pressure gauge.

I've big ol' 26X2 tires so I can't jam the tube all the way down into this bag. I have to spend time loading it just so and even then there is space wasted. If only it were 10% bigger...
Otherwise it does what you'd expect and I'm happy with it.

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